Globally it is estimated that 71 million people have chronic hepatitis C, including 3 million in the United States. Virus transmission in the US increased sharply over the last decade amongst adolescents and young adults. As a consequence, the prevalence of maternal HCV infection doubled from 2009 to 2014. Diagnosis and treatment of these infections is uncommon. Little is known about the influence of pregnancy on chronic hepatitis C. We observed that about 50% of chronically infected women experience a sharp, spontaneous drop in viremia after childbirth. Observations from the last funding period implicate immunity in this post-partum control of persistent HCV replication. First, virus suppression was associated with HLA class II DP and IFNl3 genotype. Second, appearance of new escape mutations in class I HCV epitopes during postpartum virus suppression is consistent with recovery of exhausted antiviral CD8+ T cells. Third, declining viremia coincided with expansion of functional antiviral CD4+ T helper cells. This latter observation is significant because chronic hepatitis C outside of pregnancy is marked by stable viremia and an absence of circulating functional HCV-specific CD4+ T cells. The central hypothesis of this renewal application is that recovery of CD4+ T cell help results in restoration of CD8+ T cell and B cell responses that suppress HCV replication after childbirth. Two specific aims are proposed. Aim 1 will compare CD4+ (subaim 1a) and CD8+ (subaim 1b) T cell responses in women during and after pregnancy. We predict that recovered CD4+ T cells have phenotypic, transcriptional, and functional profiles consistent with T helper (Th) and T follicular helper (Tfh) sub-populations important for development of antiviral CD8+ T cells and B cells, respectively. In Aim 1b, we predict that virus suppression is associated with expansion of functional CD8+ T cells targeting intact class I HCV epitopes. CD8+ T cells targeting intact epitopes are the most thoroughly exhausted and difficult to rescue in chronic hepatitis C. Aim 2 is to characterize HCV B cell responses in the unique setting of pregnancy. It will take advantage of an innovative tetramer comprised of the HCV E2 envelope glycoprotein to visualize and enrich antiviral B cells during and after pregnancy. This unique reagent will facilitate an analysis of whether B cells undergo changes in frequency, phenotype, transcriptional profile, and/or repertoire consistent with functional recovery and virus control. In parallel studies, whether antibody responses broaden after childbirth to neutralize contemporaneous viruses will be examined. In summary, these studies are expected to provide a detailed profile of T and B cell recovery during chronic infection, and insight into effector mechanisms relevant to development of a needed preventive HCV vaccine. More generally, we expect to fill an important gap in knowledge regarding persistent virus infections and immunity during pregnancy.